1. Field of Invention
The present invention relates to an image sensing device and its method of manufacture. More particularly, the present invention relates to a phase grating image sensing device and its method of manufacture.
2. Description of Related Art
An image-sensing device operates by converting incoming light falling upon an array of diodes into a quantity of photoelectrons. This array of diodes resembles pixels on a display panel. Each diode generates a quantity of electric charges according the intensity of light projected onto the image-sensing device. In general, incoming light passes through a color filter before entering the diodes so that the current produced by each diode represents light from a monochromatic light source.
FIG. 1 is a schematic cross-sectional view of a conventional image-sensing device. As shown in FIG. 1, a plurality of photodiodes 102 are formed above a substrate 100 and a plurality of isolation structure 104 are formed on each side of each diode 102. A smoothing layer 106 and a color filter layer 108 are sequentially formed over the diodes 102 and the isolation structure 104. The color filter layer 108 is embedded within the smoothing layer 106, forming a sandwiched structure. A condensing lens layer 112 is formed over the smoothing layer 106. The condensing lens layer 112 consists of a plurality of micro-lenses.
A conventional image-sensing device utilizes the plurality of micro-lenses in the condensing lens layer 112 to increase image-sensing sensitivity and reduce smearing. In general, the micro-lenses on the condensing lens layer 112 are formed by performing a thermal-flow procedure. However, factors such as thermal-flow temperature and pressure are extremely difficult to control in a thermal-flow procedure. Furthermore, the micro-lenses are usually made from a photosensitive resin and hence material cost is relatively high. In addition, height 114 of each micro-lens must be greater than half-width 116 at the base of the micro-lens in order to obtain a higher imaging sensitivity. However, conventional melting process for forming the micro-lenses is likely to produce a half-width 116 much greater than micro-lens height 114 due to surface tension and much variation in their dimensions.
Accordingly, one object of the present invention is to provide a phase grating image-sensing device that can avoid the problems created by a conventional method of forming a condensing layer.
A second object of this invention is to provide a phase grating image sensing device that can lower production cost and decrease processing complexity considerably.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a phase grating image-sensing device. The device includes a plurality of photodiodes, a smoothing layer, a color filter layer and a plurality of phase gratings. The photodiodes are formed on a substrate and isolated from each other by isolation structures. The smoothing layer covers the photodiodes and the isolation structures. The color filter layer is embedded within the smoothing layer forming a sandwich structure with the smoothing layer. The phase gratings are formed over the smoothing layer positioned at corresponding locations above isolation structures. The phase grating layers produce a constructive interference of light passing through the smoothing layer.
This invention also provides an alternative phase grating image-sensing device. The device includes a plurality of photodiodes, a smoothing layer, a color filter layer and a plurality of phase gratings. The photodiodes are formed over a substrate and isolated from each other by isolation structures. The smoothing layer covers the photodiodes and the isolation structures. The phase gratings are embedded within the smoothing layer positioned at corresponding locations above isolation structures. The phase gratings produce a constructive interference of light passing through the smoothing layer. The color filter layer is formed on the upper surface of the smoothing layer.
This invention provides a method of forming a phase grating image-sensing device. A plurality of photodiodes is formed over a substrate. An isolation structure is formed between the various photodiodes for isolating the photodiodes from each other. A first smoothing layer is formed over the photodiodes and the isolation structures. A color filter layer is formed over the first smoothing layer. A second smoothing layer is formed over the color filter layer. Phase grating material is deposited over the second smoothing layer. The phase grating layer is patterned to form a plurality of phase gratings. The plurality of phase gratings causes a constructive interference of light passing to the color filter layer.
This invention also provides an alternative method of forming a phase-grating image-sensing device. A plurality of photodiodes is formed over a substrate. An isolation structure is formed in-between the various photodiodes for isolating the photodiodes from each other. A first smoothing layer is formed over the photodiodes and the isolation structures. Phase grating material is deposited over the second smoothing layer. The phase grating layer is patterned to form a plurality of phase gratings. A second smoothing layer is formed over the first smoothing layer and covering the phase gratings. A color filter layer is formed over the second smoothing layer. The plurality of phase gratings causes a constructive interference of light coming in from the color filter layer.
The phase gratings of this invention are fabricated using standard CMOS procedure. Since processing conditions are much easier to control, fewer and less complicated steps than forming conventional micro-lenses are required. In addition, distance between the phase gratings and the photodiodes as well as width/height ratio of the phase gratings is easier to control. Furthermore, the phase gratings are made from metallic material, thereby lowering the production cost considerably.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.